In the use of cutting apparatus for processing logs to usable lumber, the log is forced into contact with a rotating cutting head of the apparatus that typically carries a plurality of removably clamped, elongate knives. The cutting head to which the knives are clamped typically falls into one of three classes of head shape, known in the art as disc, drum, and conical.
The apparatus spins at a relatively high rate compared to the rate of feed of the log, so that a single encounter between one of the knives of the apparatus and the log results in the displacement and removal of a relatively small portion of the log. With variations resulting from the variations in the rate of rotation relative to the rate of feed, the head geometry and the shape and configuration of the knives, this small portion is what is generally referred to in the art as a “chip” or a “flake” (hereinafter “chip”) of more or less controlled dimensions. The chip often has commercial value in itself and is not simply waste material, as it can be used in the production of manufactured wood products such as oriented strand board.
Typically, the cutting head rotates at thousands of revolutions per minute, so each chip is removed quickly, resulting in large forces being applied to the knives. To maintain chip quality, it is important to maintain the position of the knives against these forces. So the prior art has provided numerous knife shapes, typically defined in cross-sections perpendicular to the elongate axes of the knives, that work in cooperation with the clamping members to help secure the knives. For use in disc style cutting heads, the knives are often double-sided, providing two parallel cutting edges on either side of the knife. This allows turning the knife to expose a fresh cutting edge when the exposed cutting edge becomes worn.
Schmatjen, U.S. Pat. No. 5,819,826, assigned to Key Knife, Inc. of Tualatin, Oreg., describes a double-sided knife having what have often been referred to as a pair of “deflector ridges” on the bottom side of the knife, i.e., the side of the knife that faces in the direction of rotation of the cutting head. The deflector ridges project from the bottom side of the knife and therebetween form, essentially, a keyway or channel that indexes the knife to a suitably shaped inner clamping member that receives the bottom side of the knife. This indexing is an example of shaping the knife in cooperation with the clamping members to stabilize the position of the knife in the apparatus, and it also provides for easy installation of the knife into proper position.
Outer, curved transition portions of the deflector ridges further provide for guiding the flow of chips cut from the knife away from the cutting edge in such manner as to avoid damaging the chips as well as to efficiently “exhaust” the chips from the apparatus so that the required flow of material past the cutting edge is facilitated or at least not impeded.
The knife of the '826 patent has a plane of symmetry (lying mid-way between the deflector ridges) such that the knife may be turned end-for-end to expose the alternate cutting edge.
Frick et al., U.S. Pat. No. 6,951,313 shows a double-sided knife having two spaced-apart projections, where one of the projections extends from the top side of the knife, i.e., the side of the knife that faces away from the direction of rotation of the cutting head, and the other extends from the bottom side of the knife. It can be roughly compared in general configuration, for present illustrative purpose, to the knife of the '826 patent, cut along its plane of symmetry into two facing halves, where one of the halves is flipped 180 degrees. Thus, to expose the alternate cutting edge, the knife of the '313 patent is turned 180 degrees about its elongate axis instead of end-for-end. Aside from this difference, the configuration provides no apparent purpose, and it has the disadvantage that one of the projections is always non-functional and therefore is simply dead weight.
While a number of different knife configurations have been proposed, that of the '826 patent has been at least one of the most commercially successful because it provides a number of operational and manufacturing advantages. However, there remains a need for a knife assembly and chipping knife therefore providing for further improvements over the prior art.